1. Field of the Invention
The present invention relates generally to apparatus and methods for inducing an electrochemical, chemical and/or mechanical reaction on an article. More particularly, the invention pertains to methods and apparatus for treating substrates including electrodeposition of material thereonto, such as through anodizing, etching, polishing, and cleaning.
2. State of the Art
Semiconductor wafers, substrates and printed circuit boards (collectively hereinafter “semiconductor substrates”) are often coated with various materials, such as metals which are etched in later semiconductor fabrication processes to form components on the semiconductor substrates. Techniques for coating semiconductor substrates include electrodeposition, electron beam evaporator deposition, chemical vapor deposition, sputter deposition, electroless plating and the like. Electrodeposition has become a commonly used technology.
Electrodeposition or electrolytic deposition is a process which deposits a thin film of material, such as metal or metal alloy, on an article. In electrodeposition, as shown in prior art FIG. 1, an article 10 is placed in a tank 12 containing an appropriate deposition solution, such as an electrolyte solution 14, which contains ions 16 of a metal to be deposited on the article 10. The article 10 forms a cathode or is in electrical contact with a cathode 18 which is immersed in the electrolyte solution 14. The cathode 18 is connected to a negative terminal 20 of a power supply 22. A suitable anode 24 is also immersed in the electrolyte solution 14 and connected to a positive terminal 26 of the power supply 22. The electrical current causes an electrochemical reaction at the surface of the article 10 which results in the metal ions 16 in the electrolyte solution 14 being deposited on the article 10.
With semiconductor devices, it is generally desirable to deposit the metal film with a uniform thickness across the article and with uniformity of composition of the metal(s) and/or other compounds forming the metal film. However, the electrodeposition process is relatively complex and various naturally occurring forces may result in a degradation in the electrodeposition process. The electrical current or flux path between the anode and the cathode should be uniform without undesirable spreading or curving to ensure uniform deposition. Additionally, since the metal ions in the deposition solution are deposited on the article, the deposition solution becomes depleted of metal ions, which degrades the electrodeposition process. Therefore, suitable controls are required to introduce metal ions into the deposition solution in order to maintain consistency.
U.S. Pat. No. 5,516,412 to Andricacos et al. relates to an electrodeposition cell having a rack for vertically supporting a silicon substrate to be electrodeposited. An opposing wall of the cell comprises an anode. A paddle is disposed within the cell for agitating an electrolytic solution within the cell to maintain a uniform distribution of deposition material within the electrolyte solution. Furthermore, Andricacos et al. teaches that the rack can be designed to be removable for automated handling. Although Andricacos et al. addresses the control issues discussed above, the rack assembly disclosed is not conducive to high-volume manufacturing. Furthermore, Andricacos et al. does not describe, teach, or suggest any means for improving the deposition on the silicon substrate by the movement of either the anode or cathode.
U.S. Pat. No. 3,798,056 to Okinaka et al. discloses a rotating substrate holder having substrates mounted vertically about a vertical shaft. Periodic reversal of rotation is disclosed. The system relates to electroless autocatalytic plating and is unrelated to electrodeposition.
U.S. Pat. No. 3,915,832 to Rackus et al. shows apparatus for mounting and electroplating lead frames to obtain greater plate thicknesses at the lead frame ends. Lead frames are mounted radially about a tubular cathodic member which is rotated about a vertical axis while an electrolytic solution is induced to flow downwardly past the rotating mount. There is no positive control over solution movement at the lead frame surfaces.
U.S. Pat. No. 4,855,020 to Sirbola describes the electroplating of computer memory disks wherein disks are mounted on a horizontal spindle and rotated in an electrolyte bath. Coplanar anodes are spaced from each side of the disk and are coplanar to only a portion of the disk.
U.S. Pat. No. 5,472,592 to Lowery shows an electrolytic plating apparatus having a rotatable vertical shaft carrying a set of anodes. Attached to the vertical shaft is an arm about which a vertical wheel is rotated by contact with a track in the tank floor. A substrate is mounted in a vertical configuration to the wheel and is rotated by wheel rotation as the wheel travels about the vertical shaft. Virtually no control of electrolyte uniformity is exercised.
In U.S. Pat. No. 5,421,987 to Tzanavaras et al., an electroplating cell includes a horizontally rotatable anodic spray head. Electrolyte is sprayed through an intervening collimating ring onto a stationary substrate to create high turbulence at the surface. The spray head is shown with three diametrical rows of spray nozzles which cover less than the entire substrate at any time. Depending upon the location of a die in the substrate, each die may receive either one, two, or six pulses of electrolyte. To compensate, the nozzles are of differing spray design and flow rate. The limited numbers of nozzles are varied. Although not shown, it is stated that the substrate may alternatively be rotated.
Systems which are used for electrodeposition may also be used for electropolishing, electroetching, and the like. For example, U.S. Pat. No. 5,096,550 to Mayer et al. teaches attaching an article to a rotating anode positioned horizontally facedown in a polishing or etching bath. However, Mayer et al. teaches only the motion of the cathode and, since the articles are attached and treated one at a time in the anode, the apparatus of the Mayer et al. is not conductive to high-volume manufacturing.
In most electrodeposition techniques, the wafers are attached to the cathode. The attachment of wafers to the cathode can lead to significant problems, especially as the wafer quantities are increased within a single batch, control of the thickness of plated material may vary from semiconductor die to semiconductor die being manufactured on any wafer. This problem results from uniformity of metal ions and current density in the electrolyte solution adjacent the wafer surface.
It is desirable to provide highly uniform thickness and composition of deposition material on an electrodeposited article or to uniformly polish or etch an article. Furthermore, it is also desirable to do so in an apparatus capable of high-volume manufacturing, preferably using automated handling equipment.